I'm not a HB networking expert. Heck, I have little knowledge at all. I wonder if one puck failed at some time in the past or was even DOA, and the system was using the other puck for both units until that puck failed.

About the only explanation for both failing at the same time I can even imagine would be a power surge from the outboard alternator, which would probably have taken out the units themselves, or a high power field like a radar or lightning strike near the boat overloading the RF front-end.